The present invention relates generally to devices for evacuating from a gun bore the gas products associated with the firing of tank rounds. More particularly, the present invention relates to a continuous bore evacuation system which is able to expel noxious gas products and cool a gun barrel thereby improving its performance and the operators' safety.
Conventional bore evacuators are cylindrical canisters which fit around a gun barrel, creating an annular air space between the inside canister wall and the outside barrel surface. The canister is sealed against the barrel using o-rings and other mechanical fasteners, but opens into the gun bore by means of holes, or ports, which are drilled through the barrel wall at an angle. Propellant gases enter the bore evacuator after the projectile passes these bore evacuator ports. When the oxygen-poor propellant gas mixes with the air in the canister, a secondary combustion takes place. This secondary combustion raises the canister pressure two-to-three times what it would normally be were the propellant gas itself merely entrapped. The confined gas exits the bore evacuator after the projectile leaves the barrel and the pressure in the bore begins to drop back to ambient.
The bore evacuator holes are typically drilled at an angle with respect to the bore axis so that as the gas leaves the canister it is directed toward the muzzle. If the breech opening is timed correctly, this muzzle-directed flow acts to draw, or evacuate, the gas upstream of the holes. The evacuation process tends to remove any hot, solid-phase propellant residue left in the gun chamber after firing. It also reduces the amount of noxious, and potentially recombustible gas-phase propellant residue which enters the crew area when the breech is opened.
Under normal operation conventional bore evacuators are able to maintain a safe environment for the gun crew. However, in the event that the breech fails to open properly, the evacuator blow-down may be finished before any residual propellant particulates or gases are swept out of the chamber. Such a malfunction increases the possibility of a flareback in the crew area, or a hot residual ember preigniting the next round when it is loaded.
Another factor which can adversely affect the purging of bore gases in a conventional bore evacuator is a head wind, either natural, or due to the forward motion of the vehicle. With a strong head wind, bore evacuation is diminished.
Finally, the intensity of the evacuation process during blow-down has been observed to decline with the round count, owing to the drop-off in secondary combustion caused by a depletion in the oxygen content of the residual gas in the sealed canister. The replacement of residual canister gas with ambient air in a conventional bore evacuator is a slow process which can take several hours of cease-fire.